The cobondage number of a graph

A set D of vertices in a graph G = (V,E) is a dominating set of G if every vertex in V-D is adjacent to some vertex in D. The domination number γ(G) of G is the minimum cardinality of a dominating set. We define the cobondage number ${\displaystyle b_c\left(G\right)}$ of G to be the minimum cardinality among the sets of edges X ⊆ P₂(V) - E, where P₂(V) = {X ⊆ V:|X| = 2} such that γ(G+X) < γ(G). In this paper, the exact values of b_c(G) for some standard graphs are found and some bounds are obtained. Also, a Nordhaus-Gaddum type result is established.